Great winged snake

The great winged snake refers to something seen by Bran Stark through the eyes of his direwolf Summer during a wolf dream he has after the sack of Winterfell, while he and his companions are hiding in the crypt of Winterfell. At night, as Summer is exploring, he looks up,

“

The smoke and ash clouded his eyes, and in the sky he saw a great winged snake whose roar was a river of flame. He bared his teeth, but then the snake was gone. Behind the cliffs tall fires were eating up the stars.[1]

”

There has been some debate among readers as to exactly what Bran saw in the sky. Some believe that it was simply fire and smoke in the shape of a dragon, or even the red comet, while others believe that Bran saw a real dragon in the sky.